High Solids Leachbed Anaerobic Digestion (HSLAD) is a biological waste treatment system that has been successfully demonstrated for solid waste treatment in terrestrial applications. The process involves a solid phase leach bed fermentation, employing leachate recycle between new and mature reactors for inoculation, wetting, and removal of volatile organic acids during startup. HSLAD also offers a potential option for treatment of biodegradable wastes on long-duration space missions and for permanent planetary bases. This process would produce 1.5 kg of methane, 4.1 kg of carbon dioxide and 1.9 kg of compost from 7.5 kg of biodegradable solid wastes generated daily from a crew of six. HSLAD can operate at low temperature and pressure and has the potential for being a net energy producer. A detailed analysis of this process was conducted to design the system size required for a space mission with a 6-person crew. The mass, energy and water balance of the process and an equivalent system mass (ESM) analyses are presented.